Avalanche Forecast North Columbia

Tuesday 12th February 2019

Avalanche Danger Ratings Tue 12th Feb 4:09PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Considerable Danger Ratings Below Treeline: Considerable Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs

Avalanche Canada Forecaster: mbender

Date Issued:

Valid Until:

This region is currently the hotspot of human-triggered avalanche activity. Despite the cold, dry weather, dangerous avalanches continue to occur. It's a time to dial things back and stay conservative. Check out the Forecaster Blog here.

Confidence

High -

Weather Forecast

TUESDAY Night: Mainly cloudy with clear periods, light southwest wind, alpine temperature -14 CWEDNESDAY: Cloudy with sunny breaks, light west wind, alpine temperature -15 C.THURSDAY: Mix of sun and cloud, light to moderate southeast wind, alpine temperature -10 C.FRIDAY: Flurries with accumulation 5-10 cm, light south wind, alpine temperature -8 C

Avalanche Summary

Most recent avalanche activity on Monday and Tuesday has been reported as naturally triggered size 2 windlsabs between 2000 and 2300 m on all aspects.A number of significant avalanches have occurred on persistent weak layers in this region over the last several days, making it the hotspot for human-triggered avalanches at this time.On Sunday, a size 3 slab avalanche released at 1750 m on a south aspect when a sluff stepped down to the mid-January layer. Another avalanche was remote-triggered from 80 m away on an east aspect at around 1600 m.On Saturday, a snowmobiler died in a large (size 2) slab avalanche in the Bone Creek drainage (report here). It was triggered by the rider at 2100 m on a south aspect. The crown fracture varied from 15-100 cm deep, suggesting wind loading was a factor in the incident. Also on Saturday, a very large (size 3.5) natural avalanche released in a layer down 70 cm, apparently caused by icefall.On Friday, there were two skier-triggered avalanches reported, one of which was triggered remotely from 25 m away.In addition to the persistent slab avalanches, a number of wind slab avalanche were noted over the weekend, on all aspects at higher elevations.

Snowpack Summary

There are two prominent, touchy weak layers in the snowpack that have been responsible for a several dangerous avalanches, including one fatality in this region. The upper layer was buried at the end of January and lies approximately 40 cm below the surface. The lower one was buried mid-January and lies approximately 75 cm below the surface. Both comprise a mix of surface hoar and facets and may lie on top of a sun crust on southerly aspects. Both layers are highly reactive and in any given location, one or both could potentially exist in the snowpack. Wide propagation has been noted, meaning avalanches have the potential to go big (up to size 3). These weak layers are most prevalent at treeline and below treeline elevations, but may also be found in sheltered areas in the alpine.Strong northerly and easterly winds have created complicated patterns of wind-loaded snow. Many slopes are reverse-loaded or cross-loaded.Average snow depths are approximately 300 cm. Very sporadically, failures have occurred near the base of the snowpack in or close to this region. These releases have almost all been from high alpine areas, possibly triggered close to rocky features.

Persistent Slabs Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3

There are two persistent weak layers in the snowpack, buried approximately 40 cm and 75 cm below the surface. Activity is most pronounced at treeline elevations.

Any steep opening in the trees should be treated as suspect.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Wind Slabs Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Wind slabs have been reported on all aspects in exposed areas. Wind slabs at treeline elevations have the potential to step down to a persistent weak layer resulting in large avalanches.

Avoid freshly wind loaded features.If triggered, wind slabs may step down to deeper layers and result in even larger avalanches.Wind from a variety of directions has formed wind slabs in unusual locations at and above treeline.

Aspects: All aspects.

Elevations: Alpine, Treeline.

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